Washington: The US is in touch with Pakistani authorities to offer assistance in the aftermath of the horrific terrorist attack on a Peshawar school that killed 141 people, the White House said on Tuesday.

"The depraved decision that one has to make to storm a school of innocent children and open fire on them I think is a testament to how cold-blooded these extremists are," the White House Press Secretary, Josh Earnest said.

"It also is a clear indication of something that we have said on a number of occasions, which is that many of these religious extremists are carrying out attacks that have a substantial impact in terms of the number of victims on Muslims," he said in response to a question.

"Many of these extremists like to characterise their struggle as a struggle of Muslims against the western world, but that clearly is not true if the largest number of victims that we're seeing are actually Muslims. And that makes this situation all the more heart-breaking and all the more tragic," he said.

Earnest said through a variety of channels, the "US has been in touch with Pakistani officials to offer assistance".

Much of this outreach has been driven by the US Ambassador in Pakistan to a range of Pakistani officials.

The US envoy travelled with a senior Pakistani official to donate blood at the Pakistani Red Crescent today.

"That is emblematic of the kind of support that we here in the United States have for the people of Pakistan as they confront this terrible act of violence," he said.

Responding to questions, Earnest said the US remains committed to draw down of troops from Afghanistan and there is no change in the White House policy in this regard in the aftermath of the attack on a school in Peshawar.

"The President is committed to ensuring that we remain on track for the responsible draw down that he has outlined in terms of our military presence in Afghanistan," he said.

"The strategy or the mission that our troops in Afghanistan are pursuing right now is one that is focused on counter-terrorism in a way that will assist the Afghan government, but also ensure the protection of American personnel that are still in that country," he said.

"It also will entail training Afghan security forces so that they can continue the process of taking responsibility for the security situation in their country," he said.

"I do think that this scenario and this terrible event that occurred in Pakistan sort of highlights the violent tendencies of some of these extremist groups, which, in turn, underscores the need to do all that we can to strengthen and support Afghan security forces as they try to protect their country and their citizens from some of these extremist groups that aren't just carrying out acts of violence against Muslims in Pakistan, but also against Muslims in Afghanistan," Earnest said.